JP2018163186A - Optical circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical circuit board with which an electronic apparatus can operate correctly.SOLUTION: The optical circuit board comprises: a wiring board 10 including a first pad 15 on a surface thereof; an optical waveguide 20 which includes a lower clad layer 21 positioned on the wiring board 10 surface including a region where the first pad 15 is located, a core 22 positioned above the lower clad layer 21, and an upper clad layer 23 with a flat top face, the core 22 including a reflection surface 26a; a via hole 24 positioned in the optical waveguide 20 and having a first pad 15 as bottom face; and an optical element 30 positioned on the optical waveguide 20, having a flat undersurface, including at least one of a light emission part 32 and a light receiving part 33 in a position facing the reflection surface 26a on the undersurface, and having a second pad 31 in a position facing the first pad 15. The undersurface of the optical element 30 and the top face of the upper clad layer 23 are in contact with each other, and the first pad 15 is fastened to the second pad 31 in the via hole 24 with a conductive material 16.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an optical circuit board including an optical waveguide.

  Development of an optical circuit board having an optical waveguide capable of transmitting a large amount of information at a high speed has been promoted as electronic devices typified by portable game machines and communication devices have been advanced. The optical circuit board is provided on the wiring board, the optical waveguide having the lower clad layer, the core having the reflecting surface, and the upper clad layer, and the optical element mounted on the optical waveguide. It has.

JP 2012-194401 A

  In the optical circuit board, an optical signal is transmitted between the optical element and the optical waveguide. Therefore, if the optical element mounted on the optical waveguide is inclined with respect to the optical waveguide, the optical loss may increase and the optical signal may not be transmitted accurately. Thereby, there exists a possibility that an electronic device may not operate | move normally.

  An optical circuit board according to the present disclosure includes a wiring board having a plurality of first pads on the surface, a lower cladding layer located on the wiring board surface including a region where the first pads are located, and a core located on the lower cladding layer And an optical waveguide having a reflective surface that is positioned so as to cover the core on the lower cladding layer and has a flat upper surface, and the core extends obliquely with respect to the upper surface. A plurality of via holes located in the optical waveguide and having the first pad as a bottom surface, and located on the optical waveguide and having a flat lower surface, the light emitting unit and the light receiving unit are disposed at positions facing the reflecting surface on the lower surface. An optical element having at least one and having a plurality of second pads at positions facing the first pad, the lower surface of the optical element and the upper surface of the upper cladding layer being in contact with each other, It is characterized in that the pad and the second pad is fixed by a conductive material within the via hole.

  According to the optical circuit board of the present disclosure, the stability of optical signal transmission is improved between the optical element and the optical waveguide. Accordingly, it is possible to provide an optical circuit board that can easily operate the electronic device normally.

FIG. 1 is a schematic cross-sectional view illustrating an example of the first embodiment of the optical circuit board according to the present disclosure. FIG. 2 is a schematic cross-sectional view illustrating an example of the second embodiment of the optical circuit board according to the present disclosure. FIG. 3 is a schematic plan view illustrating a main part of the optical circuit board according to the present disclosure.

  An example of an embodiment of the optical circuit board according to the present disclosure will be described with reference to FIGS. The optical circuit board A according to the first embodiment includes a wiring board 10, an optical waveguide 20, and an optical element 30. The wiring board 10 has a function of positioning and fixing the optical waveguide 20 and the optical element 30 and electrically connecting the optical element 30 and the outside (motherboard or the like). An optical signal is transmitted between the optical element 30 and the outside (such as an optical device) via the optical waveguide 20. The optical element 30 performs conversion between an optical signal and an electrical signal.

  The wiring substrate 10 includes an insulating substrate 11 and a wiring conductor 12. The insulating substrate 11 has a core insulating layer 11a and a build-up insulating layer 11b. The core insulating layer 11 a has a plurality of through holes 13. The core insulating layer 11a has functions such as ensuring the rigidity of the insulating substrate 11 and maintaining flatness, for example. The core insulating layer 11a is formed, for example, by pressing a semi-cured prepreg in which a glass cloth is impregnated with an epoxy resin, a bismaleimide triazine resin, or the like, while pressing it flatly while heating.

  The buildup insulating layer 11 b includes a plurality of via holes 14. The build-up insulating layer 1b has a function of, for example, securing a routing space for the wiring conductor 12 and the like which will be described in detail later. The build-up insulating layer 11b is formed, for example, by sticking a resin film containing an epoxy resin, a polyimide resin, or the like to the core insulating layer 11a under vacuum and thermosetting the resin film.

  The wiring conductor 12 is located on the surface of the core insulating layer 11 a, the surface of the build-up insulating layer 11 b, the inside of the through hole 13, and the inside of the via hole 14. The wiring conductor 12 positioned inside the through hole 13 is electrically connected between the wiring conductors 12 positioned on the upper and lower surfaces of the core insulating layer 11a. The wiring conductor 12 positioned inside the via hole 14 is electrically connected between the wiring conductor 12 positioned on the surface of the build-up insulating layer 11b and the wiring conductor 12 positioned on the surface of the core insulating layer 11a. The wiring conductor 12 is formed of a highly conductive metal such as copper plating by, for example, a semi-additive method or a subtractive method.

  The wiring board 10 has a plurality of first pads 15 on the upper surface. The first pad 15 is connected to a second pad 31 of the optical element 30 to be described later via a conductive material 16 such as solder. Further, the wiring substrate 10 has a plurality of component connection pads 17 on the upper surface and a plurality of substrate connection pads 18 on the lower surface. The component connection pad 17 is connected to an electronic component S such as a semiconductor element. For example, an external circuit board (not shown) is connected to the board connection pad 18. The first pad 15, the component connection pad 17, and the board connection pad 18 are formed of a part of the wiring conductor 12 and are formed simultaneously with the formation of the wiring conductor 12.

  The optical waveguide 20 is located on the upper surface of the wiring substrate 10 including the region where the first pad 15 is located. The optical waveguide 20 includes a lower clad layer 21, a core 22, and an upper clad layer 23. The optical waveguide 20 has a plurality of via holes 24 with the first pad 15 as a bottom surface. The via hole 24 is formed by, for example, laser processing. The via hole 24 may be formed by exposure and development when the lower clad layer 21 and the upper clad layer 23 are formed.

  The lower cladding layer 21 has a flat shape having a thickness of 10 to 20 μm, for example. The lower clad layer 21 is formed by, for example, applying a photosensitive sheet or a photosensitive paste made of epoxy resin or polyimide resin on the wiring substrate 10 and then forming it into a predetermined shape by exposure and development, followed by thermosetting. Formed with.

  The core 22 has a rectangular cross section, and is a thin strip having a thickness of 30 to 40 μm, for example. The core 22 is formed by, for example, applying a photosensitive sheet made of an epoxy resin or a polyimide resin on the lower clad layer 21 in a vacuum state, forming it in a strip shape by exposure and development, and then thermosetting it. The refractive index of the resin forming the photosensitive sheet for forming the core 22 is larger than the refractive index of the resin forming the photosensitive sheet or paste for forming the lower cladding layer 21 and the upper cladding layer 23.

  The core 22 has a first reflecting surface 26a and a second reflecting surface 26b. The first reflecting surface 26 a and the second reflecting surface 26 b are constituted by cut surfaces extending in an oblique direction from the upper surface of the upper cladding layer 23 to the lower surface of the lower cladding layer 21. The optical element 30 is located above the first reflecting surface 26a. The first reflecting surface 26 a changes the direction of the optical signal emitted from the optical element 30 and transmits the optical signal to the core 22. Alternatively, the direction of the optical signal transmitted through the core 22 is changed to cause the optical element 30 to receive the optical signal. Further, the connector C to which the optical fiber F is connected is located above the second reflecting surface 26b. The second reflecting surface 26b changes the direction of the optical signal transmitted from the connector C and causes the core 22 to transmit the optical signal. Alternatively, the direction of the optical signal transmitted through the core 22 is changed, and the optical signal is transmitted to the connector C.

  Note that the central axis of the core 22 coincides with the central positions of the first reflecting surface 26a and the second reflecting surface 26b, and an optical signal is transmitted with reference to the central axis and the central position. Here, the central axis refers to a position where a pair of diagonal lines of the cross section of the rectangular core 22 intersect. The center position refers to a position where a pair of diagonal lines of the quadrangular first reflecting surface 26a and the second reflecting surface 26b intersect. The first reflecting surface 26a and the second reflecting surface 26b are formed by, for example, cutting the core 22 by irradiating laser light obliquely from directly above the optical waveguide 20. Alternatively, it may be formed by cutting a blade in an oblique direction from directly above the optical waveguide 20. After the core 22 is cut, surface treatment may be performed by, for example, plasma treatment or blast treatment.

  The upper clad layer 23 is located on the upper surface of the lower clad layer 21 and covers the core 22. The upper clad layer 23 has a thickness of, for example, 10 to 20 μm above the core 22 and has a flat upper surface. On the upper surface of the upper cladding layer 23, if the roughness of the surface of a region facing the light emitting part 32 or the light receiving part 33 of the optical element 30 described later is an arithmetic average roughness Ra = 10 nm or less, the optical signal is irregularly reflected. It is advantageous to reduce diffusion. Further, if the surface roughness of the other region is an arithmetic average roughness Ra = 30 to 100 nm, for example, when the optical element 30 is sealed with a resin, the resin and the upper surface of the upper cladding layer 23 are in close contact with each other. The strength can be improved, which is advantageous for reliably protecting the optical element from the external environment.

  The upper clad layer 23 is thermally cured after being coated or coated with a photosensitive sheet or paste made of, for example, an epoxy resin or a polyimide resin so as to cover the lower clad layer 21 and the core 22, exposed and developed. Is formed. The thickness of the upper clad layer 23 may be 10 to 20 μm.

  The upper surface of the upper cladding layer 23 may include a recess 25. For example, a light emitting portion 32 or a light receiving portion 33 of the optical element 30 described later is located in the concave portion 25. The recess 25 is formed by laser processing, for example. If the roughness of the bottom surface of the recess 25 is an arithmetic average roughness Ra = 10 nm or less, it is advantageous for reducing the diffuse reflection of the optical signal. The opening diameter of the recess 25 may be formed to be about 10 to 20 μm larger than the outer diameter of the light emitting part 32 or the light receiving part 33 of the optical element 30. This is advantageous for mounting the optical element 30.

  Examples of the optical element 30 include a vertical cavity surface emitting laser and a photodiode. The optical element 30 has a flat lower surface. The optical element 30 has at least one of the light emitting unit 32 and the light receiving unit 33 at a position facing the first reflecting surface 26a on the lower surface. The optical element 30 has a second pad 31 at a position facing the first pad 15 on the lower surface. The optical element 30 is located on the optical waveguide 20 with its flat lower surface and the flat upper surface of the upper cladding layer 23 in contact with each other. The second pad 31 and the first pad 15 are fixed inside the via hole 24 with a conductive material 16 such as solder.

  Thus, in the optical circuit board A of the present disclosure, the flat lower surface of the optical element 30 and the flat upper surface of the upper cladding layer 23 are in contact with each other, and the second pad 31 and the first pad 15 are connected to the via hole. 24 is fixed. For this reason, it is possible to reduce the tilt of the optical element 30 with respect to the optical waveguide 20. Thereby, it becomes easy to maintain the positional accuracy between the light emitting unit 32 or the light receiving unit 33 and the first reflecting surface 26a. As a result, it is possible to accurately transmit an optical signal between the optical element 30 and the optical waveguide 20, and it is possible to provide the optical circuit board A in which the electronic apparatus can operate normally.

  By the way, the optical element 30 may have at least one of the light emission part 32 and the light-receiving part 33 which protruded from the lower surface like 2nd Embodiment shown in FIG. In such a case, the protruding light emitting part 32 or light receiving part 33 is located in the recess 25 located on the upper surface of the upper cladding layer 23. By doing so, the optical element 30 can be positioned on the optical waveguide 20 in a state where the flat lower surface and the flat upper surface of the upper cladding layer 23 are in contact with each other. The light emitting unit 32 or the light receiving unit 33 has, for example, a quadrangular shape in plan view.

  Thereby, it becomes easy to maintain the positional accuracy between the light emitting unit 32 or the light receiving unit 33 and the first reflecting surface 26a. As a result, an optical signal can be accurately transmitted between the optical element 30 and the optical waveguide 20, and the optical circuit board B in which the electronic device can operate normally can be provided. Further, since the light emitting unit 32 or the light receiving unit 33 is located in the recess 25, the distance between the light emitting unit 32 or the light receiving unit 33 and the first reflecting surface 26a is reduced, which is advantageous for preventing diffusion of the optical signal. An optical signal can be more accurately transmitted between the optical element 30 and the optical waveguide 20.

  Note that the present disclosure is not limited to the above-described exemplary embodiment, and various modifications can be made without departing from the gist of the present disclosure. For example, in this example, the case where the opening diameter of the recess 25 is about 10 to 20 μm larger than the outer diameter of the light emitting unit 32 or the light receiving unit 33 is shown, but it may be about 3 to 5 μm. Thereby, although the mountability of the optical element 30 may be lowered, the light emitting part 32 or the light receiving part 33 and the concave part 25 protruding from the lower surface of the optical element 30 can be used as positioning means for the optical element 30 and the optical waveguide 20. By utilizing it, it can contribute to the improvement of the positional accuracy of both.

  Further, in this example, the wiring board 10 has an example in which the solder resist layer is not provided. However, the wiring board 10 is disposed on both or one of the upper surface and the lower surface of the insulating substrate 11 and the component connection pad 17. Alternatively, a solder resist layer having an opening for exposing the substrate connection pad 18 may be provided. Thereby, the damage which the wiring conductor 12 receives by the heat processing at the time of mounting the semiconductor element S can be reduced, for example.

  Furthermore, in this example, an example in which the upper surface of the upper cladding layer 23 has the recess 25 in the region facing the light emitting portion 32 or the light receiving portion 33 protruding from the lower surface of the optical element 30 is shown. May have another protrusion, the upper surface of the upper clad layer 23 may have another recess in a region facing the protrusion. Thereby, the optical element 30 is positioned on the optical waveguide 20 in a state where the flat lower surface of the optical element 30 and the flat upper surface of the upper clad layer 23 are in contact with each other regardless of the presence or absence of the protruding portion on the lower surface. Can do.

DESCRIPTION OF SYMBOLS 10 Wiring board 15 1st pad 16 Conductive material 20 Optical waveguide 21 Lower clad layer 22 Core 23 Upper clad layer 24 Via hole 26a Reflecting surface 30 Optical element 31 2nd pad 32 Light-emitting part 33 Light-receiving part A, B Optical circuit board

Claims (2)

A wiring board having a plurality of first pads on the surface;
A lower clad layer located on the surface of the wiring substrate including a region where the first pad is located, a core located on the lower clad layer, and a core located on the lower clad layer An optical waveguide having an upper cladding layer having a flat upper surface, the core having a reflective surface extending obliquely with respect to the upper surface;
A plurality of via holes located in the optical waveguide and having the first pad as a bottom surface;
Located on the optical waveguide and having a flat lower surface, the lower surface includes at least one of a light emitting unit and a light receiving unit at a position facing the reflective surface, and a plurality of positions at a position facing the first pad. An optical element having a second pad,
An optical circuit board, wherein a lower surface of the optical element and an upper surface of the upper clad layer are in contact with each other, and the first pad and the second pad are fixed by a conductive material in the via hole. .   The optical waveguide further has a recess on the upper surface of the upper clad layer, and at least one of the light emitting portion and the light receiving portion protrudes from the lower surface and is located in the recess. The optical circuit board according to claim 1.

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